Various instruments have been developed to test electrical components in vehicles for operability. Such instruments include voltmeters, ammeters and continuity testers. Some of these instruments have been incorporated into hand-held units such that these tests can be easily performed. One such hand-held instrument is a digital multimeter marketed by the assignee of the present invention under Model 2880. This instrument tests solid state electronics, computer and electronic ignition dwell, electronic and conventional ignition systems, and diodes.
Hand-held instruments have also been developed which have the capability to test certain engine sensors and ignition modules in vehicles. For example, one such hand-held instrument developed by the assignee of the present invention is shown and described in Cervas, U.S. Ser. No. 08/002,618 filed Jan. 11, 1993 for "Method and Apparatus for Testing Engine Sensors and Ignition Modules in Vehicles". The instrument described in this reference tests potentiometer-type sensors (e.g., throttle position and EGR position), temperature sensors (e.g., engine coolant, incoming air), Hall effect sensors, oxygen, knock and reluctance sensors, and ignition modules. Due to the nature of the electronic circuitry in this instrument, the instrument can test these components on different makes and models of vehicles, even though the components can have different responses during the testing process depending upon the manufacturer of the component. Moreover, this instrument combines a number of different testing capabilities in a single hand-held instrument, thus reducing the cost to the user of purchasing testing equipment and generally simplifying the overall testing process.
Other hand-held instruments have been developed which test manifold absolute pressure (MAP) sensors for certain vehicle types, such as the Thexton Model No. 127 Ford MAP/BP Sensor Tester; while other instruments have been developed which test mass air flow (MAF) sensors, such as the Kastar Model No. 280A. Manifold absolute pressure sensors and mass air flow sensors are used by the vehicle's engine performance computer to measure the air pressure or the mass of air in the manifold to maintain the proper air/fuel mixture. A malfunctioning MAP/MAF sensor can cause backfiring, hesitation, rough idle, surging, intermittent stalling, hard starting, nostarts, poor engine performance, and poor fuel economy.
However, until this point, applicant is unaware of any device which has the capability to test both manifold absolute pressure and mass air flow sensors in vehicles using a single hand-held instrument and to test these components on a variety of different makes and models of vehicles. Further, some types of MAP/MAF sensors have a voltage output when operating correctly, while others have a frequency output when operating correctly. Thus, the testing instrument must be able to test both voltage and frequency outputs from these components for different makes and models of vehicles.
Accordingly, there is a demand in the industry for a single, integral, hand-held instrument which tests mass air flow and manifold absolute pressure sensors, and tests these components on different makes and models of vehicles while the sensor remains installed in the vehicle. Further, there is a demand in the industry for a simple and convenient instrument of the abovementioned type which includes protection from overload, incorrect connection to the vehicle, and shorting, such that the instrument is not damaged through improper use.